Objectives: The National Strategic Plan for Malaria Prevention in Cameroon mainly releases on vector control by Insecticide treated nets and indoor residual spraying. Vector resistance to insecticides is therefore seen as a threat for interventions.

The objectives of the study were: (1) to evaluate the susceptibility of malaria vectors to insecticides used in vector control, (2) to identify involved resistance mechanisms and their distribution.

Methodology: A large scale programme was conducted in Cameroon from 2002 to 2006, using WHO protocol for adult bioassays as well as molecular and biochemical analyses, to evaluate susceptibility to DDT and pyrethroid insecticides in 45 field populations of Anopheles gambiae Giles and An. arabiensis Patton, 3 populations of An. funestus Giles, 2 populations of An. nili Theobald and 2 populations of An. moucheti Evans. These anopheline species are the major malaria vectors in Cameroon (300 infected bites/man/year).

Results:An. funestus, An. nili and An. moucheti were found susceptible to all insecticides, with almost 100% mortality rates. However, different patterns of resistance were seen in An. gambiae M and S molecular forms, and An. arabiensis. In the southern equatorial region, An. gambiae displayed resistance to DDT (3060% mortality rate), sometimes coupled with resistance to pyrethroids (6080% mortality rates). This resistance was mainly due to target site insensitivity resulting from a single nucleotide polymorphism in the gene encoding subunit 2 of the sodium channel. This mutation, known as kdr mutation, leads to substitution of Leucine (TTA) amino acid to Phenylalanine (TTT) or Serine (TCA). Both mutations were broadly distributed in the S molecular form, but slightly in the M form. A polymorphism was seen in discriminative nucleotides between M and S, at positions 702 and 703 of the subunit 1 of the sodium channel, but not at position 896, suggesting 3 independent mutational events and introgession between M and S forms. In the northern part of the country, both An. gambiae S form and An. arabiensis displayed low level resistance to pyrethroids and sometimes to DDT (80100% mortality rates). This resistance was attributed to elevated activity of esterases or oxidases rather than kdr mutations.

Conclusion: This is the first report of the distribution of kdr mutations in Cameroon. Current data will enable the National Malaria Control Programme to elaborate strategies for effective malaria prevention in Cameroon.